The present invention relates to a plasma processing apparatus. More particularly, it relates to a plasma processing apparatus which is preferable for performing a surface processing of a sample such as semiconductor element with the use of the plasma.
As one of the conventional plasma processing apparatuses, there exists an inductively-coupled plasma processing apparatus. In this inductively-coupled plasma processing apparatus, a radio-frequency power supply is connected to coil-shaped induction antennas which are provided along the outside of a vacuum chamber and the radio-frequency power is supplied to the induction antennas to generate the plasma. In the plasma processing apparatus which uses induction antennas like this, the coupling between the induction antennas and the plasma generated inside the vacuum chamber changes by reaction products which adhere to the inside of the processing chamber. Then, this change in the coupling gives rise to a problem of the occurrence of time-elapsed changes in such factors as etching rate, its uniformity, verticality of the etching profile, and adherence situation of the reaction products onto the etching side wall. In JP-A-2004-235545, the following method has been disclosed as a method for solving this problem. Namely, a Faraday shield, which is capacitively coupled with the plasma, is set up between the plasma and the induction antennas provided along the outside of the vacuum chamber and a radio-frequency voltage is applied to the shield. The application of this radio-frequency voltage generates a self-bias voltage on the inner wall of the vacuum chamber and an electric field existing inside the sheath draws in the ions existing within the plasma, thereby causing a sputtering on the surface of the vacuum chamber inner wall. Taking advantage of this sputtering makes it possible to suppress or remove deposition of the reaction products, thereby allowing implementation of the cleaning of the vacuum chamber inner wall. A method for controlling the radio-frequency voltage applied to the Faraday shield (i.e., the Faraday Shield Voltage, which, hereinafter, will be referred to as “FSV”) is as follows, for example. While the plasma processing of the sample is underway, the FSV is applied with such an extent as to be able to suppress the adherence of the reaction products onto the vacuum chamber inner wall. Meanwhile, at the time of the cleaning of the vacuum chamber inner wall, the radio-frequency voltage is applied which is higher than the FSV applied during the plasma processing of the sample, thereby removing the reaction products adhering onto the vacuum chamber inner wall. In order to set the above-described FSV at the set FSVs, the following control has been executed. Namely, the correlation between the FSV and the capacitance of a variable capacitor is accumulated in advance into a database. Next, the capacitance of the variable capacitor corresponding to the set FSVs is determined by making reference to the database. Then, the capacitance of the variable capacitor is made equal to the capacitance determined for the variable capacitor in the manner described above.